The long term objective of this project is to understand the process of pattern formation during Drosophila head development. The proposed work will focus on the role of the orthodenticle (otd) homeobox gene in the formation of embryonic and adult head structures. In the analysis of embryonic development, we will investigate the regulation of otd expression by the maternal morphogen bicoid in the early blastoderm. We will also examine the interactions between otd and other zygotic genes required for embryonic head development. In studying the process of adult head formation, the mechanism by which otd expression is targeted to a specific imaginal disc domain will be determined. In addition, the interaction of otd with other genes (both previously identified and novel) involved in specifying cell fate during the development of the ocelli (simple eyes) will be elucidated. Using a combination of molecular, genetic, and cellular approaches, the proposed experiments are intended to investigate the role of the otd gene during pattern formation.